One known technique for measuring the concentration of combustible components of a gas mixture involves the catalytic burning of the gas in the vicinity of an oxygen-containing suitably reactive portion of an electric bridge. In this technique the gas to be analyzed continually passes (by flow or by diffusion) over the heated catalytic portion of the bridge so that when the latter is electrically excited the balance of the bridge is disturbed. The resultant changes in the absolute value of the bridge output are then measured continually or intermittently as a measure of the concentration of the gas components.
The disadvantage of known arrangements of this type is that the bridge output voltage variation during the described conditions of gas mobility are in practice influenced not only by the heat produced by the catalytic burning but also by changes, during the measuring cycle, in the ambient temperature and in the heat conductivity of the continually moving gas mixture. This is particularly true where the concentration of the combustible components in the mixture is low and/or where the mixture has a combustible gas concentration that is dynamically variable, e.g., where water vapor or carbon dioxide are present.
While theoretically such disturbing influences can be offset to some degree by designing the bridge so that the catalytic and reference branches receive exactly the same gas flow and exhibit exactly the same geometric and electric characteristics, such conditions are extremely difficult to obtain in practice.